The present invention relates to a method of coupling two optical elements to form an optical data transmission device. In the method a first optical element must be centered with respect to a second optical element. The first element is an optical fiber. The second element is an optoelectronic component. The optoelectronic component is provided with at least one junction formed in a semiconductor body. The contact terminals are metallic layers which are provided on the surface of the semiconducting regions of the body. The active face of one end of the fiber is positioned opposite the optoelectronic component so that the transfer efficiency of the light rays transmitted by the fiber is optimum. The assembly is then retained in this position until it is enclosed in an opaque plastic material. The plastic forms an envelope which is impenetrable to external light rays.
The present invention also relates to the device obtained by this method.
In the field of telecommunications, it is known to replace coaxial electrical links between electronic devices with optical links. The optical links use optical fibers which are cabled and which connect light sources and photoreceivers.
These optical fibers, being able to carry high-frequency signals, offer the advantage that they are insensitive to external parasitic disturbances. They also have an attenuation factor which is smaller than that of the conventional coaxial cables.
For reasons concerning weight and volume and, of course, for economical reasons, the diameter of the active section of an optical fiber has nowadays become standardized at approximately 50 .mu.m. Such a fiber is generally used with an electronic component, notably a light source, which is formed a semiconductor crystal whose photoactive junction has a substantially equivalent diameter. Under these circumstances, and knowing that the acceptance angle of an optical fiber may be no larger than 10.degree., it will be evident that if the light source is not properly aimed or if the active face of the fiber, that is to say the face opposite the semiconductor junction, is not positioned with precision, the transfer or coupling efficiency is substantially reduced.
In order to achieve optimum data transmission in a fiber, therefore, it is desirable to introduce a maximum amount of light into the fiber and to position the source and the active face with high precision. It follows from this that for positioning a fiber, which is barely visible to the unskilled eye, opposite a light source, having a diameter which is equivalent to that of the fiber major technical difficulties are encountered.
When coupling an optical fiber to a photoreceiver optoelectronic component however, the problem of centering one element with respect to the other is not so difficult. This is because the photoreceiver element in known devices is generally a semiconductor diode whose junction diameter is larger than that of the section of the active face of the fiber. Thus, a margin of error is provided positioning and centering the elements. However, if the surface of the photoreceiver diode is to be reduced with respect to that of the section of the fiber, the same difficulties will be encountered as during the centering of a fiber with respect to a source.
In order to facilitate the assembly of a fiber transmission device, the optoelectronic components, or end components, are often connected to a data transfer fiber via a a pigtail fiber. The pigtail fiber is permanently connected to the component. This requires perfect centering of the pigtail fiber with respect to the optoelectronic component.
A recent type of fiber transmission devices is provided at each of its ends with an optoelectronic component which is supported by a metallic support. The component is enclosed in an opaque plastic envelope. Within this envelope and opposite optoelectronic component there is formed a duct in which one end of the transfer fiber or the pigtail fiber is inserted and secured.
It will be apparent that it is comparatively difficult to center the optoelectronic component with respect to the fiber. This is because the component is mounted on a flat surface of a comparatively wide support which serves as a base as well as a dissipator. This is also because the tolerances of the diameters of the optical fiber and the duct which are necessary for easy insertion of the fiber often require substantial clearance between these various elements.
Between the instant at which the fiber is aligned with respect to the optoelectronic component and the instant at which the fiber is secured in the duct, generally a comparatively long period of time expires during which the components must be retained in their initial position.
Only a few methods are known as present for accurately aligning a fiber and light source or receiver. In most cases, these methods involve many operations and require high mechanical precision, so that they are expensive.
A currently used method utilizes a so-called "Burrus diode". The active face of the end of the optical fiber is placed at the bottom of the cavity of the diode. However, despite the care taken in the positioning of the elements, the assembly precision remains insufficient. This lack of precision is not only caused by the aggregate tolerances of the dimensions of the cavity and the optical fiber, but also by the shrinking or shifting of the resin during its polymerization. The lack of precision thus leads to a mediocre transfer efficiency.